Catalyst for hydrogenation of unsaturated hydrocarbons

ABSTRACT

A catalyst is described for hydrogenation of unsaturated hydrocarbons, containing catalytically active amounts of Pd and optionally Ag in a support. The catalyst is characterized by the fact that the support represents a shaped body with a trilobal cross section, the lobes being provided with continuous openings. The catalysts can be produced according to a method, in which the support is impregnated with a solution of salts of Pd and optionally Ag. These salts are reduced by means of a reducing agent, whereupon the support so impregnated is washed, dried and calcined and, if reduction is not complete, the still present oxides of Pd and Ag are reduced to the corresponding metals in a hydrogen-containing atmosphere.

BACKGROUND OF THE INVENTION

The invention concerns a catalyst for hydrogenation of unsaturatedhydrocarbons.

A method for catalytic hydrogenation of acetylenic compounds with 2 or 3carbon atoms to the corresponding olefin compounds is known from EP-A-0686 615, in which a supported catalyst in the form of spheres orextrudate is used, containing palladium and silver. At least 80% of thepalladium and at least 60% of the silver are located close to thesurface of the catalyst. The catalyst preferably contains aluminum oxideas a support and 0.01 to 0.5 wt. % palladium and 0.001 to 0.002 wt. %silver. Because of the form of the support, the activity andselectivity, in relation to the weight, are relatively low. Only arelatively low space velocity can be used with this catalyst and thepressure drop is relatively high.

A catalyst, containing Pd and Ag for selective hydrogenation ofacetylene, is known from EP-A-0 689 872. The catalyst is produced bytreating a support material (preferably aluminum oxide) in the form ofspheres or cylindrical pellets, with an alkaline solution of reducingagent for Pd and Ag.

A supported catalyst for diolefin hydrogenation, containing palladium,silver and an alkali fluoride is known from EP-A-0 693 315. Sphericalpellets or cylindrical extrudates are preferably used as support.

A catalyst for hydrogenation of C₂ to C₁₀ alkynes, preferably acetylene,to the corresponding alkenes in the presence of sulfur compounds isknown from EP-A-0 738 540, which contains palladium, silver, at leastone chemically bonded alkali metal (preferably K), chemically bondedfluorine and an inorganic support (preferably aluminum oxide) in theform of pellets.

EP-A-0 732 146 describes catalysts, whose supports represent moldedbodies with a trilobal cross section and through openings. The catalystscontain iron oxide-molybdenum. oxide compounds as catalytically activecomponents. The catalysts are used specifically for oxidation ofmethanol to formaldehyde, although some other applications notdemonstrated by examples are stated (for example, hydrogenation ofacetylene and olefins).

EP-A-464 633 describes catalysts, whose support represents molded bodieswith a trilobal cross section and continuous openings (cf. FIG. 5). Thecatalysts contain a mixture of elements of groups VIII and 1B of thePeriodic Table, especially palladium and gold, as the catalyticallyactive components. They are used for conversion of olefins with organiccarboxylic acids and oxygen to unsaturated esters, especially forproduction of vinyl acetate from ethylene and acetic acid.

EP-B-591 572 describes a catalytic material in the form of particleswith a trilobal cross section and at least three continuous poreopenings, as well as a specific ratio between height of the particlesand spacing between the axes of the holes. This material is used foroxidative dehydrogenation of methanol to produce formaldehyde.

Catalysts for selective hydrogenation of diolefins and alkynes tomono-olefins and alkenes are also marketed by the applicant under thenames G-58 and G-83, which contain palladium and silver on a sphericalsupport or on a support in the form of solid pellets or extrudates (cf.data sheets “Girdler Catalysts G-58 C, G-58 D, G-58 H, G-58 I and G-83for Selective Hydrogenation”, from January 1998).

Catalysts on such supports generally have the drawback that theiractivities and selectivities are relatively low and hydrogenationreactions can only be run at relatively low space velocities. Thesecatalysts also have relatively high flow resistance.

The task underlying the present invention is to eliminate theseshortcomings. It was surprisingly found that these shortcomings could beeliminated by using a catalyst whose support has a specific shape.

The object of the invention is therefore a catalyst for hydrogenation ofunsaturated hydrocarbons, containing catalytically effective amounts ofPd and optionally Ag on a support. The catalyst is characterized by thefact that the support represents a shaped body with a trilobal crosssection, in which the lobes are provided with through openings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the catalyst of the invention.

DETAILED DESCRIPTION OF INVENTION

The catalyst according to the invention ordinarily has a geometricsurface (GS) of about 0.2 to 3 cm², preferably about 0.7 to 1.9 cm²,especially about 0.9 to 1.5 cm² per shaped body.

The ratio (R₁) between length (l) and diameter (d) of the trilobalshaped body (See FIG. 1) is preferably in the range of the following:R ₁=1/d=2−4

The ratio (R₂) between geometric surface (GS) of the shaped body andvolume of the solid fraction of the shaped body (V_(f)) preferably is:R ₂ =GS/V _(f)=0.5−20(mm⁻¹), in particular 1.4−(mm⁻¹).

Pd is preferably present in amounts of about 0.01 to 1.5 wt. % and Ag inamounts of about 0.1 to 0.5 wt. %, based on the weight of the supportmaterial, and the weight ratio between Pd and Ag is about 0.1 to 5.0.

The penetration depth of the catalytically active component (Pd andoptionally Ag) into the support as shaped bodies after reduction ispreferably wherein at least about 80% of the active components arewithin 60 to 300 μm of the surface.

The crystallite size of the Pd crystallites after reduction is about 2to 15 nm, based on 80% of the Pd crystallites, and the ratio (R₃)between the BET surface and the size of the Pd crystallites (d_(Pd)) ispreferably as follows:R ₃ =BET−S/dp _(d)=0.1−10

The size of the Pd crystallites is determined according to the COadsorption method according to the literature reference Journal ofCatalysis 25, 148–160 (1972).

Aluminum oxide, especially θ-aluminum oxide, is preferably used as thesupport. This component is generally not present in pure form, but canalso be present in other aluminum oxide forms, like α-aluminum oxide.Titanium dioxide, zirconium dioxide, silicon dioxides zinc oxide,silicon carbide or talc, however, can also be used.

The BET surface area of the support is about 1 to 300 m²/g, preferablyabout 10 to 300 m²/g, especially about 30 to 80 m²/g. The BET surfacearea is determined according to the one-point method by nitrogenadsorption according to DIN 66132.

About 40% of the BET surface area is situated in pores with a diameterof about 1570 to 80 nm and about 60% is situated in pores with adiameter of about 80 to 14 nm. Pore volume and distribution of specificsurface areas to specific pore sizes is determined according to DIN66133 (Hg porosimetry).

The trilobal shaped body used as support according to the invention areexplained in the accompanying drawing FIG. 1 wherein (d) denotes thediameter, (l) the length of the trilobal shaped body, d1 denotes thediameter of one lobe and d2 the diameter of the opening in a lobe.

The diameter (d) of the trilobal shaped body is preferably about 3 to 10mm, the length (l) is about 3 to 15 mm, and the diameter of an openingin a lobe (d2) is about 0.5 to 5 mm.

The catalysts according to the invention preferably also contain limitedamounts of alkali and/or alkaline earth metals, especially about 0.01 to0.1 wt. % (calculated as oxides).

Relative to known catalysts, the catalysts according to the inventionare characterized by high activity and selectivity. Higher spacevelocities of about 12000 to 15000 can also be used (volume parts ofreactants in the gaseous state per volume part of catalyst andhour=GSHV), compared with a space velocity of only about 3000 to 8000 ifspheres, solid pellets or extrudates are used. The catalysts accordingto the invention also exhibit lower pressure drops (up to 60% relativeto spherical or pellet-like supports (115% and 100%)) .

An object of the invention is also a method for production of thecatalysts just defined, in which the support is impregnated with asolution of salts of Pd and optionally Ag (PdCl₂, H₂PdCl₄ and AgNO₃) andthe salts reduced with a reducing agent (e.g., sodium formate, NaBH₄,hydrazine, formaldehyde, ascorbic acid, citric acid, Na acetate, oxalicacid, etc.), and preferably in an alkaline medium at temperaturesbetween about 20 and 100° C., preferably in the range from 40 to 60° C.

The reduction is preferably run in an aqueous-alkaline solution. In thisvariant of the method, the Pd and optionally Ag oxide is fixed on thesurface of the support and reduced there to the corresponding metals. Inthis manner, the penetration depth of the metal can be controlled toabout 60 to 300 μm.

As an alternative, reduction can be run with a reducing agent in anonaqueous solvent, if the reducing agent is decomposed by water. Thisis especially true for NaBH₄ and other hydrides or double-hydrides, likeLiAlH₄, LiBH₄, CaH₂ or LaH₃.

The impregnated support is generally washed, dried and calcined. Ifreduction is not complete and Pd and Ag are still present partially inthe form of their oxides, these are reduced to the corresponding metalsby heating in a hydrogen-containing atmosphere (forming). Forming,however, can also occur in the reactor, in which case only hydrogen isinitially introduced before introduction of the compounds beinghydrogenated.

The shaped bodies are generally produced by mixing the support materialwith water, a binder (like carboxymethylcellulose) and/or a lubricant(for example, an alkaline earth or aluminum stearate).

Production of the shaped bodies occurs in a pellet press with a rotaryplate, on whose periphery several openings with trilobal cross sectionare arranged. The mixture is filled into these openings (matrices) andheld from the bottom by a ram, through which three pins that lie at thesites of the openings to be produced are pushed upward during rotationof the rotary plate, On further rotation of the rotary plate, a ram witha trilobal cross section engages from the top, which is provided withopenings, into which the pins in the lower ram penetrate during pressingdown of the upper ram. The pressed shaped bodies, during furtherrotation of the rotary plate, are forced out of the matrices afterretraction of the lower ram and further advance of the upper ram. The“green” shaped bodies are dried and calcined. Pores with the desiredsite are formed in the shaped bodies.

The shaped bodies are then impregnated with a solution of salts ofpalladium and optionally silver, in which an alkaline solution is addedafter impregnation, in order to precipitate palladium and silver in theform of the corresponding oxides.

The solution of a reducing agent is then added, which reduces the oxidesto the corresponding metal. However, it is also possible to use analkaline reducing agent solution.

After precipitation of the oxides or metals of the catalytically activecomponent(s), the shaped bodies are washed, in order to eliminatesoluble salts (for example, NaCl and NaNO₃). The shaped bodies are thendried and calcined, whereupon any still present oxides of thecatalytically active component(s) are reduced to the correspondingmetals. Reduction generally occurs in a hydrogen atmosphere attemperatures from about 20 to 450° C. Reduction can also occur in areactor, in which case hydrogen or a hydrogen-containing gas isintroduced before introduction of the compounds to be hydrogenated.

Finally, an object of the invention is use of the aforementionedcatalysts for hydrogenation of unsaturated hydrocarbons, especially forselective hydrogenation of diolefins to mono-olefins or acetylenes toolefins.

The invention is explained by the following examples;

EXAMPLE 1

1000 parts by weight boehmite is mixed with 10 parts by weight water and40 parts by weight magnesium stearate to a homogeneous, pressable mass.This mass is introduced into the openings of a rotary plate of thepellet press just described, whose cross sections correspond to thedepicted shape (d=6 mm, d1=4 mm, d2=1.5 mm, l =6 mm). The shaped bodiesare then pressed, as described above, and ejected from the pellet press.The obtained shaped bodies are dried for two hours at 120° C. andcalcined for 4.5 hours at 1075° C., in which the boehmite is largelyconverted to θ-aluminum oxide (in addition to some α-aluminum oxide) Thegeometric surface is 1.3 cm² per shaped body. The BET surface area isthen determined according to DIN 66132 at 30 m²/g. The pore volume isthen determined according to DIN 66133 at 0.35 mL/g, as well as the poredistribution. 40% of the BET surface area is contained in pores with adiameter from 1750 to 80 nm, 60% of the BET surface area is contained inpores with a diameter from 80 to 14 nm.

An H₂PdCl₄ solution (0.345 parts by weight palladium) in 1150 parts byweight distilled water is rapidly added to 1000 parts by weight of theshaped bodies and slowly mixed for 5 minutes. The mixture is allowed tostand for about 60 minutes and the decolored solution then drained off.

The moist product is immediately mixed with roughly 40° C. warm 5%sodium formate solution and allowed to stand for 2.5 hours. The formatesolution is then drained off and the product is washed chloride-freewith distilled water. The product is then calcined at 540° C. for twohours.

1000 parts by weight of the calcined product is added to a solution of3.13 parts by weight AgNO₃ in 1150 parts by weight distilled water andmixed slowly for 5 minutes. The mixture is allowed to stand for twohours and the solution then discharged. The product is calcined for 2.5hours at 540° C.

The molded articles so obtained are filled into a tubular reactor thatis initially flushed with nitrogen. Hydrogen, at a temperature of 400°C., is then passed through for 8 hours, so that the palladium and silveron the shaped bodies are fully reduced. A mixture of 1.1 vol. %acetylene and 1.5 vol. % hydrogen in ethylene at a temperature of 50°C., a pressure of 2.5 MPa and a space velocity of 14000 liters ofmixture per kg of catalyst per hour is then passed through the reactor.The acetylene is 54% converted to ethylene with a selectivity of 93%.

COMPARATIVE EXAMPLE 1

A spherical catalyst support produced from θ-Al₂O₃ with a diameter of 2to 4 mm, a geometric surface of 0.3 cm², a BET surface area of 30 mg²/g,a pore volume of 0.39 mL/g and a pore volume distribution of 40% between1750 and 80 nm and 60% between 80 and 14 nm is impregnated with theH₂PdCl₄/AgNo₈ solution of example 1 and reduced, dried, calcined andformed in the same manner as described in example 1 The catalyst is usedfor selective hydrogenation of acetylene to ethylene as in example 1, inwhich the same process conditions are employed. The acetylene is 50%converted to ethylene with a selectivity of 65% at a space velocity of8000 (liter of reactants per liter of catalyst per hour).

COMPARATIVE EXAMPLE 2

The procedure of comparative example 1 was repeated with the deviationthat a catalyst in the form of 4×4 mm pellets was used, all otherconditions remaining unchanged. The acetylene was 48% converted toethylene with a selectivity of 76%.

The catalyst according to example 1 and according to comparativeexamples 1 and 2 were measured in a separate pressure loss tube (withnitrogen as measurement gas ), the following pressure loss relationbeing determined: example 1: 60%; comparative example 1: 115%;comparative example 2: 100%.

EXAMPLE 2

The procedure of example 1 was repeated with the deviation 5 that thesupport was calcined for 4.5 hours at 1020° C. and the support sotreated was coated with 0.3 wt. % palladium. The catalyst had a BETsurface area of 70±5 cm²/g, a pore volume of 0.4 mL/g with 4.71% of thesurface in pores with a diameter of 1750 to 80 nm and 76% in pores witha diameter of 80 to 14 nm. The rest of the surface pertained to poreswith a diameter of <14 nm.

The catalyst shaped bodies were formed according to example 1 in atubular reactor for 8 hours at 400° C. and exposed to a mixture ofhydrogen and a diene-containing pyrolysis gasoline (2 mol H₂, 1 moldiene) first at 30° C. and then at 60° C., a pressure of 3.0 MPa and aspace velocity of 8 volume parts liquid pyrolysis gasoline per volumepart catalyst and hour (LHSV). The composition of the pyrolysis gasolinebefore selective hydrogenation is shown in Table 1.

TABLE I MOL % benzene 38.6 toluene 22.6 o-xylene 1.7 p-xylene 4.1m-xylene 2.0 ethylbenzene 2.0 styrene 6.0 cyclohexane 0.7methylcylcohexane 1.5 hexadiene 1.2 cyclohexadiene 0.3 hexane 10.2heptane 1.4 heptene 8.9

The styrene and diene conversions, as well as the diene selectivityafter selective dehydrogenation are shown in Table II.

TABLE II Styrene Diene Diene Hours Temperature conversion conversionselectivity 24 30 98.6 99.2 81.3 48 30 98.6 98.9 81.0 12 30 98.9 99.579.8 96 60 100 100 70.7 144 60 100 99.8 69.8 170 60 100 99.8 69.2

COMPARATIVE EXAMPLE 2

The procedure of example 2 was repeated, with the deviation thatcatalysts in the form of spheres with a diameter of 2 to 4 mm with apalladium coating of 0.3%, a geometric surface of 0.3 cm², a BET surfacearea of 70±5 cm²/g, a pore volume of 0.5 mL/g and a pore distribution asthe catalyst of example 2 were exposed to pyrolysis gasoline with thecomposition stated in Table I at an initial temperature of 30° C. andlater 60° C., a pressure of 3.0 MPa and an LHSV of 4. The styrene anddiene conversions, as well as the diene selectivity after selectivehydrogenation, are shown in Table III.

TABLE III Styrene Diene Diene Hours Temperature conversion conversionselectivity 24 30 83.7 81.7 60.9 48 30 84.5 61.7 59.6 72 30 81.7 81.957.9 96 60 95.7 91.7 50.3 144 60 95.6 91.5 45.5 170 60 95.7 91.6 40.8

EXAMPLE 3

According to the procedure of example 1 of EP-0 314 024-A1, a commercialtitanium dioxide (P-25 Degussa) is homogenized in an intensive mixerwith addition of about 55 wt. % water and 14 wt. % isopropyl titanatefor 45 minutes. After several hours of drying at 110° C., the TiO₂ massis subjected to size reduction, mixed with aluminum stearate aspelletizing agent and pressed into shaped bodies with a trilobal crosssection according to example 1 (dimensions as in example 1).

The TiO₂ shaped bodies are calcined for 3 hours at 550° C. in anoxidizing atmosphere.

The geometric surface was 1.3 cm² per shaped body, the BET surface area36 m²/g, the pore volume 0.39 mL/g, 3.7% of the BET surface areapertained to pores with a diameter from 1750 to 80 nm, and 95.8% poreswith a diameter of 80 to 14 nm.

The TiO₂ support was spray-impregnated with an 8% aqueous sodium formatesolution (30 mL formate solution per 100 g support). The support sopretreated was then spray-impregnated with the same volume of a 2.5%aqueous PdCl₂ solution. The support shaped bodies were immersed in aformate solution, filtered by suction and washed chloride-free forcomplete reduction of the noble metal. After drying at 100° C., theywere calcined for 6 hours to a final temperature of 400° C. Promotionwith silver was then carried out. For this purpose, thepalladium-containing TiO₂ shaped bodies were impregnated at roomtemperature with silver nitration solution, dried at 110° C. andcalcined for another 6 hours to a temperature of 360° C. The palladiumcontent was 0.21 wt. % , the silver content 0.12 wt. %.

The catalyst was used at a pressure of 0.15 MPa, a temperature of 120°C. and a LHSV of 15 h⁻¹, with a molar ratio H₂/diene of 2:1 forselective hydrogenation of a liquid diene-containing mixture with thecomposition

-   -   85.7 mol % paraffin    -   11.1 mol % mono-olefin    -   0.85 mol % dienes    -   2.40 mol % aromatics.        Diene conversion was 80% at a selectivity of 85%.

COMPARATIVE EXAMPLE 3

The procedure of example 3 is repeated, with the deviation that solidpellets, with dimensions of 4.5×4.5, were used instead of the trilobalshaped bodies, and they were coated in the same manner as in example 3with the catalytically active metals. The support had a BET surface areaof 33 m²/g and a pore volume of 0.2 mL/g, 51% of the BET surface areapertaining to pores with a diameter from 1750 to 80 nm, 87.3% of thepores with a diameter from 80to 14 nm. The catalysts contained 0.213 wt.% Pd and 0.27 wt. % Ag.

The catalyst was used for selective hydrogenation of thediene-containing mixture used in example 3 (LHSV=10 H⁻¹, T=120° C.,pressure=0.15 MPa, molar ratio H₂: diene=4:1).

The diene conversion was 70% at a selectivity of 60%.

1. A catalyst for hydrogenation of unsaturated hydrocarbons comprisingcatalytically active amounts of palladium on a support, wherein thesupport is a shaped body with a trilobal cross-section, wherein lobes ofthe trilobal shaped body are provided with openings passing therethroughand wherein a ratio between a length and a diameter of the trilobalshaped bodies is from about 2:1 to about 4:1.
 2. The catalyst of claim 1further comprising catalytically active amounts of silver.
 3. Thecatalyst of claim 2 wherein the palladium comprises from about 0.01 to 1weight percent and the silver comprises from 0.1 to 0.5 weight percentof the catalyst and wherein a weight ratio between the palladium and thesilver in the catalyst is from about 0.1:1 to about 5:1.
 4. The catalystof claim 1, wherein a ratio between a geometric surface of the shapedbody and a volume of the shaped body is from about 0.5:1 to about 20:1.5. The catalyst of claim 1, wherein a ratio between a geometric surfacearea of the shaped body and a volume of the shaped body is from about1.4:1 to about 4:1.
 6. The catalyst of claim 1, wherein the palladiumcomprises from about 0.01 to about 1 weight percent of the catalyst. 7.The catalyst of claim 1 wherein the support comprises aluminum oxide. 8.The catalyst of claim 7 wherein the aluminum oxide comprisessubstantially theta aluminum oxide.
 9. The catalyst of claim 1 whereinthe BET surface area of the support is from about 10 to 300 m²/g. 10.The catalyst of claim 1 wherein the BET surface area of the support isfrom about 30 to 80 m²/g.
 11. The catalyst of claim 1 wherein a diameterof the trilobal shaped body is from about 3 to 10 nm, a length is fromabout 3 to 15 nm and a diameter of an opening in a lobe of the trilobalshaped body is from about 0.5 to 5 nm.
 12. The catalyst of claim 1further comprises from about 0.01 to about 0.1 weight percent of amaterial selected from a group consisting of an alkali metal, analkaline earth metal or mixtures thereof, wherein the weight percent iscalculated in the form of oxides.
 13. A method for production of thecatalyst of claim 1 comprising preparing a shaped body having a trilobalcross-section in which lobes of the shaped body are provided withopenings passing therethrough, impregnating the shaped body with apalladium salt solution, reducing the palladium salt solution to apalladium oxide with a reducing agent, washing, drying, and calciningthe impregnated, shaped body and reducing the palladium oxide to acorresponding palladium metal.
 14. The method of claim 13 comprisingimpregnating the shaped body with a silver salt and reducing the silversalt to silver metal.
 15. The method of claim 13 wherein the reducing ofthe palladium salt is accomplished in an alkaline medium at atemperature from about 20 to about 100° C.
 16. The method of claim 13wherein the reducing of the palladium salt is accomplished in an aqueousalkaline solution.
 17. A catalyst for hydrogenation of unsaturatedhydrocarbons comprising catalytically active amounts of palladium on asupport, wherein the support is a shaped body with a trilobalcross-section, wherein lobes of the trilobal shaped body are providedwith openings passing therethrough and wherein the catalyst has ageometric surface from about 0.2 to 3 cm².
 18. The catalyst of claim 17,having a geometric surface from about 0.7 to 1.2 cm².
 19. The catalystof claim 17, having a geometric surface from about 0.9 to 1.5 cm².
 20. Acatalyst for hydrogenation of unsaturated hydrocarbons comprisingcatalytically active amounts of palladium on a support, wherein thesupport is a shaped body with a trilobal cross-section, wherein lobes ofthe trilobal shaped body are provided with openings passing therethroughand wherein the catalyst further comprises palladium crystallites aftercatalyst reduction wherein at least about 80 percent of the palladiumcrystallites have a crystallite size from about 2 to 15 nm.
 21. Acatalyst for hydrogenation of unsaturated hydrocarbons comprisingcatalytically active amounts of palladium on a support, wherein thesupport is a shaped body with a trilobal cross-section, wherein lobes ofthe trilobal shaped body are provided with openings passing therethroughwherein a BET surface area of the support is from about 1 to 300 m²/gand wherein up to about 40 percent of the BET surface area is containedin pores with a diameter from about 1750 to 80 nm and at least about 60percent of the BET surface area is contained in pores with a diameterfrom about 80 to 14 nm.
 22. A catalyst for hydrogenation of unsaturatedhydrocarbons comprising catalytically active amounts of palladium on asupport, wherein the support is a shaped body with a trilobalcross-section, wherein lobes of the trilobal shaped body are providedwith openings passing therethrough, and wherein the catalyst comprisespalladium crystallites after catalyst reduction, wherein a ratio betweena BET surface area of the catalyst and a size of the palladiumcrystallites is from about 0.1:1 to about 10:1.